The present invention relates generally to a brake shift interlock for a transmission shift lever and more specifically to a brake shift interlock in combination with an ignition interlock.
Many of the present day automotive vehicles having automatic transmissions use electronically controlled mechanisms to establish the operating condition of the transmission. These control systems typically include solenoids, switches, and electronic circuitry.
For reasons of safety and government regulation, it is required that these automatic transmissions incorporate transmission shift-lock capability wherein the transmission shift lever and the ignition switch have limited movement unless certain conditions are met. In accordance with the shift-lock function, when starting the vehicle, the transmission shift lever can be moved out of the park position only if the driver presses on the brake pedal and if the key is turned so as to be in the run position. Various systems have been proposed and utilized to achieve a combined brake shift interlock and ignition switch interlock function, but these prior art systems have been complicated and expensive in construction. Current systems which combine both the brake shift interlock and ignition switch interlock functions utilize at least two sensors for detecting different positions of a park position switch and an ignition switch. Traditionally, at least two sensors are utilized because of a range of motion in which to clear the lock mechanism when shifting from a park position to a non-park position. For instance, the brake shift interlock is required to maintain a lever releasing condition until the transmission shift lever is completely or fully out of park position. On the other hand, the ignition switch interlock is required to not change state unless the transmission shift lever is completely or fully in the park position.
It would be desirable, therefore, to provide a brake shift interlock system which reduces the complexity of these systems and provides greater robustness and reliability during construction and operation of the system.
The present invention overcomes the disadvantages of the prior art approaches by providing a brake shift interlock system for a vehicle which includes a minimum of additional mechanical componentry and complexity needed to effect the desired locking of the transmission gear shift. The brake shift interlock system has a transmission shift lever and a brake pedal. The system comprises a shift solenoid which provides a mechanical stop for the transmission shift lever while in a first position. A park position sensor is included for sensing whether the transmission shift lever is in a predetermined shift position and a brake pedal position sensor is included for sensing whether the brake pedal is in a predetermined pedal position.
The invention provides a latch and driver circuit electrically connected to the shift solenoid, the park position sensor, and the brake pedal position sensor, wherein the latch and driver circuit energizes the shift solenoid when the transmission shift lever is in the predetermined shift position and when the brake pedal position sensor senses the predetermined pedal position. Furthermore, the latch and driver circuit continuously energize the shift solenoid for as long as the brake pedal continues to be in the predetermined pedal position even after the transmission shift lever is no longer in a full-park position. The latch and driver circuit de-energizes the shift solenoid when the brake pedal is no longer in the predetermined pedal position.
It is also an object of this invention to provide a method of operation for the brake shift interlock system wherein the invention senses a predetermined shift position of the transmission shift lever. The predetermined shift position of this invention is preferably the full-park position. Additionally, this invention senses a predetermined pedal position of the brake pedal, wherein the predetermined pedal position of the brake pedal is a depressed position. Moreover, this invention energizes a shift solenoid within the brake shift interlock system when both the brake pedal is in the predetermined pedal position and the transmission shift lever is in the predetermined shift position. This invention energizes the shift solenoid for as long as the brake pedal continues to be in the predetermined pedal position even if the shift lever moves out of the Park position. The shift solenoid is de-energized when the brake pedal is applied and the transmission shift lever is not in the full-park position.
These and other advantages, features and objects of the invention will become apparent from the drawings, detailed description and claims which follow.